ABSTRACT
The modern concept of rock support is to dissipate a part of the energy released from the rock mass in order to achieve a stable status in underground excavations. This is particularly true in high-stress rock masses. In this chapter, the loading conditions and the requirements for rockbolts are first discussed in order to understand why energy-absorbing support devices are needed in high-stress rock conditions. Testing methods for examining the performance of rockbolts are also briefly presented to facilitate the reading of the test results of the rockbolts in the subsequent sections. Seven types of energy-absorbing rockbolts, which are either used for dynamic rock support in practice or still in the stage of trials, are introduced. All energy-absorbing bolts are characterized by their high load and displacement capacities compared with conventional rockbolts such as fully encapsulated rebar bolts. They dissipate energy either through ploughing/slippage in the grout or auxiliary elements such as anchors and sleeves (cone bolt, Garford bolt, Durabar, Yield-Lok, Roofex and He bolt) or through stretching of the bolt steel (D-Bolt). The dynamic load of an energy-absorbing rockbolt based on ploughing/slippage is usually smaller than its static load, while the static and dynamic loads of the stretching-based rockbolt (D-Bolt) are approximately the same.
